Printed circuit boards (PCBs), upon which a large number of discrete components are mounted, are widely used in electronics. Conductive traces are generally disposed on and/or within the PCB. The conductive traces are typically made by patterning (typically by etching) thin copper foil. A PCB populated with electronic components is known as a printed circuit assembly (PCA). PCBs are generally double sided, with through-hole plating that electrically connect opposite sides.
PCBs are typically formed by lamination of multiple insulating, and optionally additional conductive layers. Conductive layers are typically made of thin copper foil. Insulating dielectric prepreg layers typically laminated together with epoxy resin. PCBs are often coated with a solder mask, which is often green in color. There are many different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit design. Well-known prepreg materials used in the PCB industry include FR-2 (phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass and polyester), G-10 (woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (woven glass and epoxy), CEM-4 (woven glass and epoxy), and CEM-5 (woven glass and polyester).
The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a “blank PCB”) then removing unwanted copper after applying a temporary mask (for example, by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.
In recent years, a trend toward decreasing PCB size has put a premium on space usage on PCBs. One approach has been to embed components within the body of the PCB as the part of PCBs laminated structure. For example, 3M Company markets a line of embeddable capacitors under the trade designation 3M Embedded Capacitance Material (3M ECM).
Yet, the number of components that are available in embeddable form remains small in number, and there remains a need for components that can be embedded within PCBs.